The path of a carbon dioxide molecule from a gas-condensate reservoir, through the amine plant and back down into the subsurface for storage. Case study: The Sleipner area, South Viking Graben, Norwegian North Sea

Abstract

Abstract The Sleipner Vest Field, which came on stream in 1996, is the largest gas/condensate field in the Sleipner area. Having a higher carbon dioxide content (9 mole%) than the gas export quality specifications of 2.5 mole% CO2, it was necessary (prior to development approval)to find some way of handling the excess CO2 without damaging the natural environment.An amine plant was installed at the Sleipner T platform to extract the CO2 from the reservoir gas, which was then injected and stored some 800–1000m below sea level and 2.5 km east of the Sleipner A platform in the Utsira Formation - a water-filled acquifer.Up until now (mid 2005), about seven million tonnes of CO2 have been injected. The stored CO2 has been monitored using time lapse seismic to confirm its behaviour and evaluate (i) whether any of it has migrated towards the Sleipner installations, potentially leading to corrosion problems for well casing; or (ii) whether any of it has leaked into the overburden seal, the ocean or the atmosphere. The results show that neither of these eventualities has occurred. Introduction This paper highlights the pathway of the carbon dioxide from its generation in the source rock to its accumulation in the reservoir, its partial extraction in an amine plant, and its compression and injection into the Utsira Formation aquifer for long-term storage. The following important issues have continually been in focus since the Sleipner Vest field started productionoptimization of the amine plant to increase its CO2extraction capacityincreasing and stabilizing the injection capacitymonitoring the behaviour of the stored CO2 The various challenges that arose during production have all been solved, and today the method of CO2 extraction in an amine plant and its injection into a shallow aquifer for storage has proved to be an excellent example of how to produce reservoirs with high CO2 contents while limiting environmental consequences. The experiences achieved in the Sleipner's CO2 handling project since 1996 have been widely accepted and important for other CO2 storage projects.The first oil and gas development in the Barents Sea, an area which requires high environmental standards, has been made possible based on these experiences, [Ref.1]. Production history The Sleipner Vest gas/condensate field is situated on the Sleipner Terrace (to the east of the Utsira High) in the southeastern part of the Viking Graben (North Sea) (Fig. 1).The field is located 240 km west-southwest of Stavanger in production licences PL046 and PL029, co-owned by Statoil (the operator), ExxonMobil, Norsk Hydro and Total E&P Norway. The in-place hydrocarbon volumes are 160 GSm3 gas and 70 MSm3 of unstabilized condensate. Gas/condensate production in the Sleipner area started in 1993 from the Sleipner Øst Ty Field, Fig. 1.The gas is transported, together with Troll Field gas, through the Zeepipe and Statpipe pipelines to continental Europe. The condensate is piped to Kårstø (Norway) where it is separated into stabilized condensate and natural gas liquid (NGL) products. When plateau production was reached in 1994, a dry gas-recycling program was initiated at the Sleipner Øst Ty Field to remobilize the condensate and increase its recovery from about 50% to over 70%.Massive dry gas re-injection started in 1996, when the nearby gas/condensate field, Sleipner Vest, came on stream to fulfil gas sales commitments.